As the name implies, these disorders are associated with disruption in a person's circadian rhythm. They affect people in one of two ways and are therefore divided into two categories, Delayed Sleep Phase Syndrome (DSPS) and Advanced Sleep Phase Syndrome (ASPS). In both cases, light therapy and possibly melatonin can be used to reset the biological clock.
This form is most frequently characterized by difficulty falling asleep until quite late and by trouble waking up at conventional times, and is most often seen in adolescents and young adults.
This form most often affects the elderly and is characterized by falling asleep too early in the evening and awakening too early in the morning.